This invention relates to a cooking station for gas ranges whose burners are operated with super-stoichiometric combustion air free mixing, consisting of a burner head arranged in a burner tray or pan, a mixing pipe connected with the burner head, through which the gas and combustion air mixture is supplied to the burner head, and a gas nozzle arranged in front of the mixing pipe from which the gas jet comes out and suctions in the entire combustion air.
Currently customary cooking stations for gas ranges as a rule are equipped with injector burners which work with sub-stoichiometric primary air premixing. The additional secondary air necessary for complete combustion is diffused uncontrolled or unregulated into the flames forming at the mixture outlet openings in the burner head. This has a negative effect in the entire working area upon the efficiency of the burner, that is to say, the supplied heat energy is not used in an optimum fashion both in the nominal load and the partial load spread. Besides, the sub-stoichiometric premixing flame forms a comparatively large nitrogen oxide share in the waste gas which mostly escapes into the place where the equipment is set up. The so-called small adjustment heat load can also be improved. The heat load or stress on a cooking station burner is adjustable in a phaseless manner between a large position, that is to say the nominal heat load, and a minimum, small adjustment, the small adjustment heat load. According to the applicable standard, the latter may not exceed a certain part of the nominal heat load. This requirement is met by customary cooking station burners, but practical experience shows, especially in ranges operated with natural gas, that the small adjustment heat load is a point that is worthy of improvement.
Additional requirements for the cooking station burner are derived from the fact that natural gases with varying Wobbe index are being increasingly distributed in the Federal Republic of Germany which are combined in the so-called second gas family. Because gas change should be possible within a gas family, without making any changes on the burner, a cooking station burner must, within the largest possible operating spread of gases with varying Wobbe indexes, the so-called Wobbe index spread, meet the requirements regarding ignition, combustion quality, and flame stability especially in connection with the small adjustment heat load.
It is known from the technical literature that, by means of super-stoichiometric premixing, that is to say, by supplying the entire air involved in combustion to the burner through the mixing pipe, without secondary air admission to the flames, we can achieve a waste gas which is poor in harmful substances and we can at the same time achieve better energy utilization, especially in the partial load spread.
But no burner is known in which the problems, which appear on the basis of the large combustion air volumes, have been solved in design terms, especially regarding insufficient flame stability.
We do know of a cooking station whose burner works with super-stoichiometric primary air admixture, excluding secondary air admission to the flame. But the burner of this cooking station is very expensive in terms of design and construction because it has two separate nozzle mixing pipe devices for the formation of the gas and air mixture for a main flame and a holding flame or pilot flame.
Because the waste gases from this burner mostly flow to the outside through narrow grooves in the burner tray and mostly give heat off there to the bottom of the pot, there has been no efficiency increase to the degree expected.
The purpose of the invention is to create a cooking station in this category of equipment whose burner, with simple design means, will permit optimum utilization of the supplied heat energy both during nominal heat load and in the partial load spread. The burner should reveal good ignition, steady flame peformance, perfect combustion, and a waste gas poor in harmful substances at nominal and small adjustment heat loads within a large utilization spread of gases with differing Wobbe indexes.
This problem is solved according to the invention.
The object of the invention accordingly is a cooking station whose burner is operated with super-stoichiometric air premixing whereby the air number or coefficient, that is to say, the ratio between the combustion air supplied and the volume of air needed for complete combustion, is about 1.05 to 1.70.
The burner head according to the invention reveals two flame opening rings which are perforated, which are arranged concentrically with respect to the burner head axis, which are resistant to heat and reducing as well as oxidizing atmosphere, preferably made of aluminum containing and nickel-free chromium steel or ceramics, through which the gas and air mixture escapes and is ignited. The outlet openings on the inner flame opening ring have a hydraulic diameter of less than 1.2 millimeters, preferably 1.2 millimeters to 0.8 millimeters, whereas those on the outer flame opening ring have a diameter of more than 1.2 millimeters, preferably 1.2 millimeters to 3 millimeters.
In this way we achieve the following:
In the state of inertia or rest, which is obtained shortly after ignition, the flames burn on the inner flame opening ring. In the process they heat the outer flame opening ring so much that a metallic flame opening ring will begin to glow. The previously mentioned hydraulic diameters of the flame outlet openings on the one hand will prevent the flames burning on the inner ring from backfiring and on the other hand make sure that, if necessary, the flames burning initially on the outer ring, can backfire. Flame formation on the outer ring, that is to say, a "migration" of the flames from the inner to the outer ring, however, is not possible so long as the outer flame opening ring is still heated or glowing. The stability of the flames burning on the inner ring is particularly effectively guaranteed by the action of the hot or glowing outer flame ring.
When the cooking station is open, the burner head is embedded in a burner pan or tray which is so shaped that the speed of the waste gases flowing to the outside is substantially constant at all stations; this guarantees good heat transfer through convection to the bottom of the pot and the burner tray. The bottom of the pot is heated not only through convection but also through heat radiation which starts from the surface of the tray and from the outer flame opening ring.
The material or the wall thickness of the burner tray is so selected that it has only a small heat capacity and therefore stores only little heat, which has a good effect on the heating time of the pot.
Coating the burner tray underside with a material with low emission capacity and providing a reflector located below the burner tray prevents any major heat volumes from being irradiated or reflected down.
As supporting surfaces for the pot we have several carrying ribs attached to the burner tray as well as the burner head whose lid touches the pot. The direct cooling of the burner head by the pot standing on it has a favorable effect on the operation of the burner.
If the cooking station is covered by a cover plate according to the further version, then we get an improved cooking start efficiency compared to conventional gas range cooking stations.
By virtue of the super-stoichiometric air premixing, the burner of the cooking station according to the invention reveals all of these conditioned advantages, especially waste gas poor in harmful substances and efficiency improvement compared to known burners.
In spite of the large air volumes involved in combustion, we can, with simple design and construction means, achieve extremely stable flames in a large load spread so that, even when we have a low small adjustment heat load, we can get hygienically perfect combustion.
This applies to the use of all gases with various Wobbe indexes within a gas family.